import math

x1 , y1 , x2 , y2 = map(float,input().split())

a = abs(x1-x2)
b = abs(y1-y2)

ans = math.sqrt(a**2 + b**2)

print('{:.9f}'.format(ans)) import math math x1 , y1 , x2 , y2 = map(float,input().split()) x1 map(float,input().split()) map float input().split() ().split () input split y1 x2 y2 a = abs(x1-x2) a abs(x1-x2) abs x1-x2 x1 x2 b = abs(y1-y2) b abs(y1-y2) abs y1-y2 y1 y2 ans = math.sqrt(a**2 + b**2) ans math.sqrt(a**2 + b**2) math.sqrt math sqrt a**2 + b**2 a**2 a 2 b**2 b 2 print('{:.9f}'.format(ans)) print '{:.9f}'.format(ans) '{:.9f}'.format '{:.9f}' format ans y1 , x2 , y2 = map(float,input().split()) map(float,input().split()) y1 y2 = map(float,input().split()) map(float,input().split()) y2 ans = math.sqrt(a**2 + b**2) math.sqrt(a**2 + b**2) ans x2 , y2 = map(float,input().split()) map(float,input().split()) x2 x1 , y1 , x2 , y2 = map(float,input().split()) map(float,input().split()) x1 b = abs(y1-y2) abs(y1-y2) b a = abs(x1-x2) abs(x1-x2) a
import math

x1 , y1 , x2 , y2 = map(float,input().split())

a = abs(x1-x2)
b = abs(y1-y2)

ans = math.sqrt(a**2 + b**2)

print('{:.9f}'.format(ans))
